Device and method for influencing the operating mode of at least one vehicle stabilizing device arranged in a vehicle

ABSTRACT

A plurality of vehicle stabilizing devices which operate according to different strategies and which actuate, independently of the driver, brake actuators which are assigned to the vehicle wheels, in order to stabilize the vehicle are arranged in the vehicle. The vehicle is equipped with at least one switchable differential lock in the drive train. The differential lock assumes a non-switched operating state, a first operating state in which the differential lock is preselected, and a second operating state in which the differential lock is switched. When the differential lock assumes the first operating state, some of the vehicle stabilizing devices, other than that vehicle stabilizing device which, by actuating the brake actuators independently of the driver, prevents the vehicle wheels from locking during a braking operation, are influenced in terms of their operating mode. When the differential lock assumes the second operating state, all the vehicle stabilizing devices are influenced in their operating mode. The operating mode of the vehicle stabilizing devices is influenced in such a way that the actuation of the brake actuators which is independent of the driver does not occur.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a device and a method for influencing theoperating mode of at least one vehicle stabilizing device which isarranged in a vehicle.

Vehicle stabilizing devices are known nowadays in a wide variety offorms. Examples of these are brake assistants (BAS), brake slipcontrollers (ABS), traction slip controllers (ASR), electronic tractionsystems (ETS) or vehicle movement dynamic controllers (ESP). Thesevehicle stabilizing devices have one thing in common: they actuate,independently of the driver, at least brake actuators which are assignedto the vehicle wheels, in order to stabilize the vehicle. These vehiclestabilizing devices have proven effective in the road mode. Theycontribute to better control of vehicles and to reducing accidents.

Against this background it is understandable that, if possible, a largeproportion of the vehicles taking part in road traffic should beequipped with such vehicle stabilizing devices. This also applies tovehicles with all-wheel drive or off-road vehicles because the advancedpossibilities of the vehicle stabilizing devices specified above shouldalso be made available in these vehicles. Finally, it is desirable tomake road traffic as safe as possible and to reduce the risk ofaccidents as far as possible.

In vehicles with all-wheel drive, to be more precise in off-roadvehicles in which the long-proven mechanical locks are used for hard orextreme off-road use, which is referred to as the off-road mode,problems may occur if the vehicle is operated with the mechanical locksactivated and one of the vehicle stabilizing devices specified aboveactuates, independently of the driver, one of the brake actuatorsassigned to the vehicle wheels during such an operating state of thevehicle, that is to say a braking intervention which is independent ofthe driver is carried out. These aforesaid off-road vehicles have threemechanical differential locks. As a result, when differential locks areactivated, one hundred percent mechanical coupling of the front and rearaxle differentials are ensured and furthermore the front and the rearaxles are also mechanically coupled by means of the differential lock inthe transfer gear. If the braking intervention which is independent ofthe driver is carried out in the case of such a mechanical coupling ofthe axles, this leads to the braking forces being displaced via theaxles which are now “rigid”. In other words, the braking force is notonly generated at the one vehicle wheel whose brake actuator isactuated, but also at the other vehicle wheels owing to the “rigid”axles. This leads to an undesired vehicle behavior.

The prior art discloses various devices which are concerned with theproblems described above.

For example, German document DE 196 41 101 A1 discloses a method forcontrolling a longitudinal lock of an all-wheel-driven vehicle. In orderto bring about better driving comfort, the longitudinal lock isautomatically closed when there is a load change. However, apparatusessuch as an antilock brake system or a vehicle movement dynamic systemare preferred in order to ensure undiminished driving stability andbraking stability of the vehicle. That is to say, when the chassiscontrol or brake control is actuated, the longitudinal lock is not takeninto account, with respect to the load change. Moreover, when there is abraking operation initiated by the driver of the vehicle, if thelongitudinal lock is closed, it is opened immediately. In summary, thefollowing can be inferred from German document DE 196 41 101 A1: if abraking intervention which is dependent on a driver or a brakingintervention which is independent of a driver is to be carried out, thisbraking intervention is given priority and the longitudinal lock isopened up or even not closed in the first place.

European document EP 0 191 131 B1 is further prior art. In thisdocument, a road vehicle is proposed with an antilock protection inwhich the front wheels are controlled individually and the rear wheelsare controlled according to the select-low principle. The driven rearaxle is provided with a differential lock which can be switched on. Inorder to increase the stability of the vehicle when the differentiallock is engaged, an apparatus is provided which detects the engagementof the lock and, when the lock is engaged, switches over the logic ofthe antilock protection electronic system of the front axle fromindividual control (IR) to a modified individual control (MIR), a selectlow control (SLR) or some other control logic which attenuates the yawmoment and steering torque, at the front wheels. From European documentEP 0 191 131 B1 which is to be considered as forming the generic type,the following can thus be inferred: the operating mode of a vehiclestabilizing device which actuates, independently of the driver, at leastbrake actuators which are assigned to the vehicle wheels, in order tostabilize the vehicle, is influenced in terms of its operating mode assoon as the longitudinal lock assumes an operating state other than thenon-switched operating state.

The vehicle which is described in European document EP 0 191 131 A1 isonly equipped with a vehicle stabilizing device, specifically with anantilock protection device. Proposals as to what procedure should beadopted if the vehicle is equipped with a plurality of vehiclestabilizing devices which actuate, independently of the driver, at leastbrake actuators which are assigned to the vehicle wheels, in order tostabilize the vehicle, are not given in this document.

Against this background, the following object presents itself: theintention is to provide a device which, in vehicles with all-wheel driveor in off-road vehicles which are equipped both with differential locksand with vehicle stabilizing devices which actuate, independently of thedriver, at least brake actuators which are assigned to the vehiclewheels, in order to stabilize the vehicle, allows an unrestrictedoff-road mode of these vehicles, while simultaneously supporting thedriver for as long as possible in critical driving situations which maypossibly occur.

Unrestricted off-road mode is to be understood to mean the following: avehicle with all-wheel drive or an off-road vehicle which is equippedwith vehicle stabilizing devices, which actuate, independently of thedriver, at least brake actuators which are assigned to the vehiclewheels, in order to stabilize the vehicle, despite the presence of thevehicle stabilizing devices is to behave—in the off-road mode with thelocks activated—like a vehicle which does not have such vehiclestabilizing devices and in which, consequently, no adverse effects ofthe vehicle behavior as a result of braking interventions which areindependent of the driver can occur during the off-road mode.

This object is achieved by means of claimed features.

According to the invention, in order to achieve the above object in avehicle in which a plurality of vehicle stabilizing devices whichoperate according to different strategies are arranged which actuate,independently of the driver, at least brake actuators which are assignedto the vehicle wheels, in order to stabilize the vehicle, and which isequipped with at least one switchable, in particular mechanical,differential lock in the power train, which differential lock assumes anon-switched operating state, and in addition to this non-switchedoperating state a first operating state which is different from thenon-switched operating state and in which the differential lock ispreselected, and a second operating state which is different from thenon-switched operating state and the first operating state and in whichthe differential lock is switched, as soon as the differential lockassumes the first operating state, some of the vehicle stabilizingdevices are influenced in terms of their operating mode, and as soon asthe differential lock assumes the second operating state, all thevehicle stabilizing devices are influenced in terms of their operatingmode.

This procedure according to the invention, which corresponds to astepped procedure, has the following advantage: as long as thedifferential lock is in the non-switched operating state, there is norigid coupling between the wheels of a vehicle axle or between the axlesof the vehicle, and consequently braking forces which are increased at awheel cannot be transmitted to other wheels. This means that the brakeactuators which are assigned to the vehicle wheels cannot be actuatedappropriately for requirements without there being the risk ofdisruptive effects occurring in the process. There is no need toinfluence the vehicle stabilizing devices in their operating mode, andconsequently their entire functionality is available to support thedriver. In contrast, as soon as the differential lock is in thepreselected operating state, i.e. in the transition phase between thenon-switched operating state and the switched operating state, it can beassumed that within a foreseeable time a rigid coupling may occurbetween the individual wheels or axles, thus displacing braking forcesbetween the individual wheels. Although, in the preselected operatingstate, the differential lock is not yet activated, its activation willtake place within a short time period. In order to prevent a possiblyoccurring, disruptive displacement of braking forces, some of thevehicle stabilizing devices are already influenced at this stage interms of their operating mode. This is a preventative measure, since thetime at which the differential lock is activated last and it becomesnecessary to influence the vehicle stabilizing devices in terms of theiroperating mode cannot be determined in advance precisely. Only some ofthe vehicle stabilizing devices are influenced in terms of theiroperating mode, specifically those whose support in the transition phaseand the associated vehicle state can be dispensed with. The remainingvehicle stabilizing devices are not influenced in their operating mode,and are thus available to support the driver. These are vehiclestabilizing devices whose support should not be dispensed with, even inthe transition phase and the associated vehicle state. As a result,stabilization of the vehicle is ensured to a minimum degree. Only if thedifferential lock is in the switched operating state are the remainingvehicle stabilizing devices also influenced in their operating mode,meaning that all the vehicle stabilizing devices are made available tothe driver, at any rate to an only still restricted degree or even areno longer made available. This measure avoids possible displacement ofbraking forces owing to the coupling between the wheels. The support tothe driver by the vehicle stabilizing devices can be dispensed with insuch operating states of the vehicle, there are no speeds present, sincein such operating states stabilizing braking interventions which areindependent of the driver are usually not necessary.

The operating mode of the vehicle stabilizing devices is advantageouslyinfluenced here in each case in such a way that theactuation—independent of the driver—of the brake actuators which areassigned to the vehicle wheels, by the respective vehicle stabilizingdevice does not occur. As a result, if the differential lock assumes anoperating state other than the non-switched operating state, i.e. iseither preselected or switched or activated, it is ensured that none ofthe brake actuators which are assigned to the vehicle wheels is actuatedindependently of the driver, and an increase in braking force ordecrease in braking force does not take place at any of the vehiclewheels, which increase or decrease could give rise, in this operatingstate of the differential lock, to a disadvantageous effect on anothervehicle wheel or another vehicle axle and would thus bring about anundesired and eventually disruptive effect on the movement of thevehicle. The advantageous effects—described above—of the respectivevehicle stabilizing device corresponds to a deactivation of therespective vehicle stabilizing devices.

As already explained, with the apparatus according to the invention, thevehicle stabilizing devices are influenced incrementally in theiroperating mode. The following procedure advantageously presents itself:if the differential lock assumes the first operating state, with theexception of that vehicle stabilizing device which, by actuating thebrake actuators independently of the driver prevents the vehicle wheelslocking during a braking operation, all the vehicle stabilizing deviceswhich are arranged in the vehicle are influenced in terms of theiroperating mode. As soon as the differential lock assumes the secondoperating state, this vehicle stabilizing device is also influenced interms of its operating mode. This measure ensures that this vehiclestabilizing device, which is known to correspond to a brake slipcontroller, is made available in its full scope to the driver for aslong as possible for supporting purposes.

The vehicle which has a front axle and a rear axle is advantageously avehicle with all-wheel drive. In this vehicle, both the front axle andthe rear axle are each effectively assigned a differential lock. That isto say the front axle has a differential gear mechanism withdifferential lock, referred to below as front axle differential gearmechanism and front axle differential lock, and the rear axle has adifferential gear mechanism with differential lock, referred to below asrear differential mechanism and rear differential lock. Furthermore, inthe vehicle, a further differential lock is effectively arranged betweenthe front axle and the rear axle. In other words: the vehicle underconsideration has a transfer gear, composed of a differential gearmechanism and a differential lock, for dividing the torque between thefront axle and the rear axle. This differential gear mechanism and thisdifferential lock are referred to below as longitudinal differentialgear mechanism and longitudinal differential lock.

According to the invention, the operating mode of the vehiclestabilizing device is influenced as soon as the differential lock whichis arranged between the front axle and the rear axle, i.e. thelongitudinal differential lock, assumes an operating state other thanthe non-switched operating state. The influencing of the operating modeof the vehicle stabilizing device is aimed at the longitudinaldifferential lock for the following reason: in a vehicle with all-wheeldrive which is equipped with the abovementioned three differentiallocks, said locks are preselected and activated in the sequencelongitudinal differential lock, then rear axle differential lock and,finally, front axle differential lock. That is to say, the longitudinaldifferential lock is inevitably always activated irrespective of whichof the three differential locks is activated last. Consequently, for thedecision as to whether or not it is necessary to influence the operatingmode of the vehicle stabilizing device, it is sufficient to monitorwhether the longitudinal differential lock is preselected.

In a transition of the differential lock from the non-switched operatingstate into the switched operating state, the first operating state isassumed before the second operating state. Here, the switched operatingstate corresponds to the second operating state. In the non-switchedoperating state, the differential lock is not activated. In the switchedoperating state, the differential lock is activated. The first operatingstate which is specified above corresponds to a transition operatingstate between the non-switched operating state and the switchedoperating state.

Advantageously, at least one brake slip controller (ABS) and one brakeassistant (BAS) and/or one traction slip controller (ASR) and/or oneelectronic traction system (ETS) and/or one vehicle movement dynamicscontroller (ESP) are arranged in the vehicle as vehicle stabilizingdevices. In other words: the vehicle is equipped in all cases with abrake slip controller and can have any desired combination of thefurther vehicle stabilizing devices.

If the differential lock assumes the first operating state, i.e. ispreselected, the braking assistant and/or the traction slip controllerand/or the electronic traction system and/or the vehicle movementdynamics controller are influenced in their operating mode, i.e.deactivated. That is to say the brake slip controller remainsuninfluenced in terms of its operating mode, as a result of which astable vehicle behavior is ensured at least when braking occurs.Depending on which of the further vehicle stabilizing devices specifiedabove the vehicle has, said devices are influenced, i.e. deactivated, interms of their operating mode.

If the differential lock assumes the second operating state, i.e. isactivated, in addition to the vehicle stabilizing devices whoseoperating mode was already influenced when the differential lock was inthe first operating state, the brake slip controller is also influencedin terms of its operating mode. That is to say, the brake slipcontroller and the braking assistant and/or the traction slip controllerand/or the electronic traction system and/or the vehicle movementdynamics controller are influenced in terms of their operating mode. Inspecific terms, this means: both the brake slip controller and thefurther vehicle stabilizing devices which are present in the vehicle areinfluenced in terms of their operating mode.

The operating state of the differential locks can advantageously be setby the driver by activating a switching means. The following sequenceapplies to the setting of the at least one further operating state ofthe differential locks which is different from the non-switchedoperating state: first, the operating state of the differential lockwhich is effectively arranged between the front axle and the rear axle,the longitudinal differential lock, and then the operating state of thedifferential lock which is effectively assigned to the rear axle, therear axle differential lock, and then the operating state of thedifferential lock which is effectively assigned to the front axle, thefront axle differential lock, are set.

It has proven particularly advantageous that the driver is informedabout the operating state of the differential lock and/or about theoperating mode of the vehicle stabilizing device which is arranged inthe vehicle and/or about possibly occurring faults by means of a displaymeans. In particular, the displaying of faults which occur at thedifferential locks, or which occur owing to the operation of thedifferential locks, is of particular interest. The monitoring of faultsfor the differential lock is advantageously carried out as a function atleast of a signal which represents the operating state of thedifferential lock.

As already mentioned, the operating state of the differential lock canbe set by the driver by activating a switching means. The followingfault monitoring system advantageously presents itself: a fault isdetected if, after activation of the switching means in order to set anoperating state of the differential lock which is different from thenon-switched operating state, the predefined time period has passedwithout the differential lock assuming this operating state.

This fault monitoring can also be improved as follows: if a firstpredefined time period has passed without the differential lock assumingthe second operating state, a vehicle stabilizing device with whichlocking of the wheels is prevented during a braking operation isinfluenced in terms of its operating mode. In addition or as analternative, if a second predefined time period has passed above apredefined vehicle speed without the differential lock assuming thesecond operating state, this situation is communicated to the driverand/or a fault entry is made in a memory medium.

It is particularly advantageous that the device according to theinvention or the method according to the invention can be implemented ina simple and cost-effective way in vehicles with all-wheel drive.

Further advantages will emerge from the following description and theappended drawing. At this point it is to be noted that any desiredcombination of the subclaims, and thus of the subject matters describedin the subclaims, are conceivable.

The exemplary embodiment will be explained in more detail with referenceto the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a vehicle with all-wheel drive or anoff-road vehicle in which the device or the method according to theinvention is used,

FIG. 2 is a schematic view of the device according to the invention, and

FIG. 3 is a schematic view of the method according to the inventionwhich takes place in the device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The schematic view in FIG. 1 shows a vehicle 100 which has vehiclewheels which are referred to by 101 ij in an abbreviated notation. Thisabbreviated notation has the following meaning: the index i indicatesthat the wheel is a front wheel (v) or a rear wheel (h). The index jindicates whether it is a left-hand (l) or a right-hand (r) wheel. Ifthis abbreviated notation is used in conjunction with other components,it has the same meaning there. In addition, the vehicle has an engine102 a and a transmission 102 b which interacts with it.

The vehicle 100 will be a vehicle with all-wheel drive, or an off-roadvehicle which is correspondingly equipped. For this reason, the vehicle100 is equipped with a transfer gear 105 which is composed of adifferential gear mechanism 103 a and a differential lock 104 a. Thetransfer gear 105 is operatively connected to the engine 102 a via thetransmission 102 b, and serves the purpose of dividing the torquebetween the front axle VA and the rear axle HA. For this purpose, thetransfer gear 105 is operatively connected to an axle gear 106 which isassigned to the rear axle HA and which is composed of a differentialgear mechanism 103 h and a differential lock 104 h. In addition, thetransfer gear 105 is operatively connected, for this purpose, to an axlegear 107 which is assigned to the front axle VA and which is composed ofa differential gear mechanism 103 v and a differential lock 104 v.

At this point, the following should be noted with respect to the view ofthe transfer gear and the axle gear selected in FIG. 1: the view in theform of a comprehensive block which illustrates the transfer gear andthe axle gears, with a diagonal dividing line, is intended to indicatemerely that the respective gear mechanism is composed of two individualcomponents, specifically in each case a differential gear mechanism andan associated differential lock. This representation merely has thefunction of representing the basic design of the gear mechanisms and isnot intended to have a technologically active or functional meaning interms of the axles or shafts which are connected to the comprehensiveblock.

For the sake of better understanding, a more detailed explanation ofsome of the components specified above will be given at this point.

In vehicles, differential gear mechanisms are used on the drive axle inorder to compensate the rotational speed differences of the drivenwheels which occur when cornering or are due to a different tire radiuswhich is caused, for example, by fabrication tolerances of the tires ora different tire air pressure. Using differential gear mechanisms thusavoids forced slip between the wheels of the drive axle.

In roadway conditions with different traction at the drive wheels, thewheel with the low coefficient of friction determines the transmissiblepropulsion force of the vehicle and slips when there is an excess drivetorque. This loss of traction can be reduced by a locking differentialor by a differential lock (the two designations locking differential anddifferential lock are equivalent in meaning). Nowadays, a distinction ismade between, on the one hand, positively locking, switchabledifferential locks and, on the other hand, frictionally locking,automatic differential locks. Positively locking differential locksconnect both halves of the axle of the drive axle rigidly to one anotherin the activated, i.e. switched, state, which leads to forced slip andstress when cornering. In other words: with positively lockingdifferential locks, a hundred percent mechanical, i.e. rigid coupling ofthe two wheels of the drive axle is implemented. Positively lockingdifferential locks are also referred to as mechanical differentiallocks. In the context of the device and method according to theinvention, the vehicle under consideration is to be equipped with suchmechanical differential locks.

In comparison with a vehicle which is driven by a single axle, adual-axle vehicle with all-wheel drive has three differential gearmechanisms 103 a, 103 h and 103 v with the same number of differentiallocks 104 a, 104 h and 104 v. A differential gear mechanism 103 v and103 h with assigned differential lock 104 v and 104 h is provided oneach of the two vehicle axles VA and HA. In addition, the vehicle has atransfer gear 105 which is arranged between the front axle and the rearaxle and which is implemented as differential gear mechanism 103 a withdifferential lock 104 a. The two vehicle axles VA and HA are driven viathe centrally arranged transfer gear 105 with a torque which is dividedinto two equal halves, or even divided asymmetrically.

To clarify once more the problems on which the device and the methodaccording to the invention are based: if a vehicle with all-wheel driveis equipped with switchable mechanical differential locks, the vehicleaxles VA and HA are mechanically coupled if the longitudinaldifferential lock 104 a is activated. If the front axle differentiallock 104 v is activated, the wheels of the front axle are mechanicallycoupled. If the rear axle differential lock 104 h is activated, thewheels of the rear axle are mechanically coupled. Consequently, awheel-specific braking intervention, either an increase or a decrease inbraking pressure, which is carried out independently of the driver,leads, when the differential locks are activated, to the mechanicallycoupled vehicle wheels and/or vehicle axles being influenced, and thusto the vehicle behavior being undesirably influenced. The device andmethod according to the invention are aimed at avoiding this.

In FIG. 2, block 203 represents the vehicle stabilizing device ordevices arranged in the vehicle. Depending on the degree of equipment ofthe vehicle, the block 203 is either an individual vehicle stabilizingdevice or a plurality of vehicle stabilizing devices which operateaccording to different strategies. To be brief: the vehicle is equippedwith at least one vehicle stabilizing device.

The form of the representation selected in FIG. 2 is not intended tohave a restrictive effect. It is also conceivable for an independentblock 203′ to be provided for any individual device of the vehiclestabilizing devices which operate according to different strategies,said block being operatively connected, in accordance with block 203, tothe other components illustrated in FIG. 2.

In a general form, i.e. irrespective of the specific configuration ofthe vehicle stabilizing device or devices arranged in the vehicle, theblock 203 is connected to a block 201. The block 201 is the sensorsystem which is necessary for the operation of the vehicle stabilizingdevice or devices and which provides the block 203 with the respectivelyrequired input variables Sx for carrying out the correspondingregulating or control operation.

In addition, the block 203 is connected in a general form to a block 204and to a block 205. The block 204 represents the brake actuators whichare assigned to the individual vehicle wheel, which actuate using thesignals FBx by the vehicle stabilizing device for carrying outwheel-specific braking interventions which are independent of thedriver. If necessary, the vehicle stabilizing device receives feedbackfrom the brake actuators about their operating state by means of thesignals BFx.

For the sake of simplicity, in FIG. 2 the brake actuators 204 ij whichare respectively assigned to the vehicle wheels 101 ij are combined toform a block 204. In addition, it is to be noted that the brakeactuators may be part of a hydraulic or an electrohydraulic or apneumatic or an electropneumatic or an electromechanical brake system.In the first four brake systems mentioned, the brake actuators areactuated valves via which brake medium is fed to a wheel brake cylinderor carried away from it. In the case of the brake system mentioned last,the brake actuators are electrically activated servomotors whoseactivation can generate a braking torque at the individual vehiclewheels. If the expression brake pressure is used in this description,this is not intended to constitute a restriction. In a correspondingway, the term braking force or some other term which describes a brakingeffect can also be used, allowing for the necessary technical changes.

The block 205 represents means for influencing the drive torque which isoutput by the engine. The drive torque which is to be output is set as afunction of the signals FMx which are fed to the means 205 from thevehicle stabilizing device. If necessary, the vehicle stabilizing devicereceives feedback from the means 205 about its operating state by meansof the signals MFx. The means 205 can be, for example, a throttle valvewhich is assigned to the engine, or an injection device.

As is apparent below from the specific description of the vehiclestabilizing devices arranged in the vehicle, the operating mode of theindividual vehicle stabilizing device determines whether said deviceactuates the block 204 and/or the block 205.

The vehicle stabilizing devices have, considered in the context of thedevice or method according to the invention, the following in common: inorder to stabilize the vehicle, they actuate, independently of thedriver, at least individual brake actuators which are assigned to thevehicle wheels. In other words: they carry out wheel-specific brakinginterventions which are independent of the driver and by means of whichbraking pressure is increased or decreased.

The vehicle stabilizing device or the vehicle stabilizing devices maybe, for example, the following:

A vehicle movement dynamics controller, which is known by theabbreviation ESP (Electronic Stability Program). Such a vehicle movementdynamics controller stabilizes the vehicle about its vertical axis. Thetransverse dynamics are therefore controlled. For this purpose, the setpoint value for the yaw rate of the vehicle is determined from thesteering angle which is set by the driver, and the vehicle speed whichis determined. This set point value is compared with an actual value forthe yaw rate which is determined using a suitable sensor. During thiscomparison, the deviation of the actual value from the set point valueis determined. Depending on this deviation, set point slip changes aredetermined for the individual wheels, with which changes the set pointslip which is to be set at the respective wheel is modified. In order toset the modified set point slip values, braking interventions arecarried out independently of the driver at the individual wheels 101 ijof the vehicle by activating the respectively assigned brake actuators204 ij. The respective actual slip is approximated to the predefined setpoint slip for each individual wheel by means of these wheel-specificbraking interventions. The brake pressure at individual wheels isusually increased by means of these braking interventions. As a result,a yaw moment which acts on the vehicle and which causes the vehicle torotate about its vertical axis is brought about, as a result of whichthe actual value of the yaw rate is approximated to the associated setpoint value. Engine interventions with which the engine torque which isoutput by the engine is reduced can also be carried out in order tosupport the wheel-specific braking interventions which are carried outindependently of the driver.

In the case of a vehicle movement dynamics controller, wheel speedsensors, a steering angle sensor, a transverse acceleration sensor, ayaw rate sensor and a sensor for determining the admission pressurewhich is set by the driver are combined in the block 201. The block 203actuates the brake actuators, block 204, and the means for influencingthe engine torque which is output by the engine, block 205.

An electronic traction system (ETS). This electronic traction system isactivated if one of the drive wheels slips in a predefined speed range.The slipping wheel is braked, using braking interventions which areindependent of the driver, until the wheel speed difference between thedriven wheels of a vehicle axle drops below a predefined value. Thebraking intervention simulates, at the slipping wheel, the largercoefficient of friction of the opposite driven wheel. At the wheel whichis at the higher coefficient of friction, the torque which is output isincreased by the braking torque, and a locking effect is consequentlyproduced. If an excessively large traction slip occurs when cornering ina predefined speed range, the vehicle instability which is caused as aresult of this is decreased by a braking intervention on both sides.

The block 201 represents wheel speed sensors in the case of anelectronic traction system. The block 203 actuates the brake actuators,block 204.

A traction slip controller (ASR). Using a traction slip controller, thevehicle is stabilized during a starting-up process in such a way thatthe driven wheels are prevented from slipping. As a result,interventions in the longitudinal dynamics are carried out. The tractionslip controller operates, for example, according to the followingprinciple: an actual value for the wheel slip is determined for each ofthe driven wheels. This actual value is compared with a threshold value.As long as the actual value is lower than the threshold value,instability does not occur, and no stabilizing interventions arenecessary. However, if the actual value is higher than the thresholdvalue, instability occurs and stabilizing interventions are necessary.If the threshold value is exceeded, the propulsion which is desired bythe driver by activating the accelerator pedal, for example as a resultof an excessively low coefficient of friction of the underlying surface,cannot be brought about. An excess of driving torque is present at thedriven wheels, which causes driven wheels to slip, thus leading to aloss of lateral guidance. In order to restore the lateral guidance,stabilizing interventions are carried out. The stabilizing interventionsare primarily braking interventions which are carried out at the drivenwheels independently of the driver. Braking pressure is increased at thedriven wheels by means of these braking interventions, as a result ofwhich the excess of driving torque which is present at the driven wheelsis decreased. Depending on the condition of the underlying surface, forexample what is referred to as a μ-split situation may be present, thebraking interventions which are independent of the driver are carriedout on a wheel-specific basis, i.e. in a way which is adapted to therespective situation for each of the driven wheels. In order to supportthe braking interventions, it is also possible to carry out engineinterventions with which the engine torque which is output by the engineis reduced. Of course, other variables for detecting spinning drivenwheels can also be evaluated.

In the case of a traction slip controller, wheel speed sensors and meansfor preparing variables which represent the operating state of theengine, for example the engine torque which is output by the engine, arecombined in the block 201. The block 203 controls the brake actuators,block 204, and the means for influencing the engine torque which isoutput by the engine, block 205.

A braking assistant (BAS). A braking assistant is intended to supportthe driver while he carries out braking operations, to the effect that,in the case of a braking operation which is initiated by the driver, themaximum possible braking force or braking deceleration in this situationis generated for this purpose activation of the brake pedal which isperformed by the driver is monitored. If a predefined activation of thebrake pedal is detected, braking interventions, which increase thebraking force present at the individual vehicle wheels, are carried outindependently of the driver. This can be done, for example, by feedingin brake pressure. The brake pressure is fed in until the locking limitis reached at the individual wheels. As a result, the lateral guidancefor the individual wheels is retained together with optimum utilizationof the braking effect. In order to detect the predefined activation ofthe brake pedal, for example the deflection angle or the deflection pathof the brake pedal or the speed with which the brake pedal is activatedare evaluated. A predefined activation occurs if a respectivelyassociated threshold value is reached or exceeded.

In the case of a braking assistant, wheel speed sensors and means fordetermining the activation of the brake pedal are combined in the block201. The block 203 actuates the brake actuators, block 204.

A brake slip controller (antilock brake system, ABS). Using a brake slipcontroller, the vehicle is stabilized during a brake operation to theeffect that locking of the braked wheels is avoided. As a result, thelongitudinal dynamics are stabilized. A brake slip controller operates,for example, according to the following principle, in each case anactual value for the wheel slip is determined for all the wheels of thevehicle. For each of the wheels, this actual value is compared with athreshold value. As long as the actual value is lower than the thresholdvalue, no instability is present and no stabilizing interventions arenecessary. However, if the actual value is higher than the thresholdvalue, instability occurs and stabilizing interventions are necessary.If the threshold value is exceeded, there is a risk of the individualwheels of the vehicle locking because, for example, the underlyingsurface has a very low coefficient of friction. A locking wheel can nolonger transmit any lateral guiding force, as a consequence of whichthere is a loss of lateral guidance. In order to restore the lateralguidance, stabilizing interventions are carried out. These stabilizinginterventions are braking interventions which are carried outindependently of the driver and with which the fed-in brake pressure isdecreased at the wheels at which there is a risk of locking. Since thebehavior of the individual wheels is different depending on thecondition of the underlying surface, the braking interventions which areindependent of the driver are carried out in a way which is adapted in awheel-specific fashion, i.e. for each individual vehicle wheel. Ofcourse, other variables can also be evaluated in order to detect a riskof locking.

In the case of a brake slip controller, the block 201 represents wheelspeed sensors. The block 203 actuates the brake actuators, block 204.

The above statements relating to the individual vehicle stabilizingdevices are exemplary and are not intended to have a restrictive effect.Of course, modified embodiments of the individual vehicle stabilizingdevices are also intended to be included. The present listing of vehiclestabilizing devices which carry out braking interventions which areindependent of the driver in order to stabilize the vehicle is also notintended to be conclusive. Of course, further vehicle stabilizingdevices which operate according to this principle may be arranged in thevehicle. Moreover, the vehicle can also be equipped with vehiclestabilizing devices which carry out other interventions than brakinginterventions which are carried out independently of the driver.

Block 202 represents a switching means with which the driver can set theoperating state of the differential locks 104 which are arranged in thevehicle. That is to say, by activating the switching means 202, thedriver can predefine whether the differential locks which are arrangedin the vehicle are to assume the non-switched operating state or anoperating state which is different from this non-switched operatingstate. It is conceivable that, by activating the switching means 202,the operating state can be set for a single differential lock or for apredefined combination of differential locks or for all the differentiallocks together. The following combinations result depending on thesequence with which the differential locks which are arranged in avehicle with all-wheel drive are preselected or activated: the singlelongitudinal differential lock, the longitudinal differential locktogether with the rear axle differential lock or all three differentiallocks simultaneously. The switching means 202 is configured in acorresponding way in order to be able to set these combinations.

Since the longitudinal differential lock is always preselected oractivated in the case of a preselection or activation of thedifferential locks, the following configurations are possible based onthe longitudinal differential locks:

None of the differential locks is preselected. Consequently, all of thevehicle stabilizing devices which are specified above are active, andnone is deactivated. Braking interventions which are independent of thedriver take place in an unrestricted fashion.

The longitudinal differential lock is preselected. In this case, all thevehicle stabilizing devices are deactivated with the exception of thebrake slip controller. Only the brake slip controller can still carryout braking interventions which are independent of the driver.

The longitudinal differential lock is activated. In this case, all thevehicle stabilizing devices which are arranged in the vehicle, that isto say also the brake slip controller, are deactivated. No brakinginterventions which are independent of the driver can be carried out anymore.

On the one hand, the switching means 202 outputs a signal DS start whichis fed to the block 203 and to the differential locks 104. On the otherhand, a signal DS active, which is fed to the block 203, is output bythe block 202. At this point it is to be noted that, in FIG. 2, thedifferential locks 104 a, 104 v and 104 h which are arranged in thevehicle 100 are combined to form a block 104, for the sake ofsimplicity.

If at least one of the differential locks is to assume, or if thedifferential locks are to assume, an operating state which is differentfrom the non-switched operating state, in particular the first operatingstate, the driver must place the switching means in a first position, asa result of which a first signal level, for example a low level, isoutput for the DS start signal. The DS start signal is active in thiscase. As a result, at least one of the differential locks assumes, orthe differential locks assume, the first operating state, i.e. they arepreselected. In addition, the operating mode of some of the vehiclestabilizing devices combined to form the block 203 is influenced, i.e.some of these vehicle stabilizing devices are deactivated.

Owing to the sequence which has already been described and in which thedifferential locks are preselected, the longitudinal differential lockis firstly preselected by the driver placing the switching means in thefirst position. The vehicle stabilizing devices which are deactivatedare the vehicle movement dynamics controller and/or the electronictraction system and/or the traction slip controller and/or the brakingassistants.

If the differential locks are to assume the non-switched operating stateagain, the driver must move the switching means into a second position,as a result of which a second signal level, for example a high level, isoutput for the DS start signal. That is to say, the signal DS start isreset and is inactive. The longitudinal differential lock is no longerpreselected. The vehicle stabilizing devices which are specified aboveare activated again.

The respective state of the differential locks 104 is signaled back tothe switching means 202 by means of signals Sp state. These signals areprocessed using a logic which is contained in the switching means 202.If the signals Sp state signal that at least one of the differentiallocks has assumed the activated state, the logic for the signal DSactive outputs a first signal level, for example a low level (2 volts).As a result, the operating mode of all the vehicle stabilizing deviceswhich are contained in the vehicle and which carry out brakinginterventions which are independent of the driver is influenced, i.e.all of these vehicle stabilizing devices are deactivated. In thespecific case, the first signal level is output if the longitudinaldifferential lock is activated. As a result, the brake slip controlleris also deactivated. Depending on the further vehicle stabilizingdevices with which the vehicle is equipped, the vehicle movementdynamics controller and/or the electronic traction system and/or thetraction slip controller and/or the braking assistant remaindeactivated.

If, on the other hand, the signals Sp state signal that none of thedifferential locks is in the switched operating state, i.e. all thedifferential locks are deactivated, the logic outputs a second signallevel, for example a high level (4 volts) for the signal DS active. As aresult, the operating mode is again influenced only for some of thevehicle stabilizing devices mentioned above, i.e. again only some ofthese vehicle stabilizing devices are deactivated.

Lighting means, for example light-emitting diodes, are advantageouslymounted on the switching means and are used to indicate whether adifferential lock, or which differential lock, is preselected or active.

At this point it is to be noted once more that the sequence with whichthe differential locks can be preselected or activated is defined asfollows: at first the longitudinal differential lock, then the rear axledifferential lock and then the front axle differential lock.

Block 206 represents a display means with which the driver is informedabout the operating state of the differential locks 104 and/or about theoperating mode of the vehicle stabilizing device or devices 203 whichare arranged in the vehicle and/or about possibly occurring faults. Forthis purpose, signals SAx which contain information about the operatingstate of the differential locks or possibly about faults which occur atthem are fed to the display means 206 from the block 202. In addition,signals FAx which contain information about the operating mode of thevehicle stabilizing devices which are arranged in the vehicle and whichcarry out braking interventions which are independent of the driver inorder to stabilize the vehicle, or about faults occurring at saiddevices, are fed to the display means 206 from the block 203. Thisinformation is conditioned or evaluated in the display means andpresented to the driver.

If it is detected in block 202 that a fault is present for one of thedifferential locks, a signal Sp fault is generated in the block 202 andis fed to the block 203 and a fault entry is made in the block 203 as afunction of said signal.

FIG. 3 illustrates a method according to the invention in a flowchartwhich represents a switching logic.

The method according to the invention starts with a step 301 which isfollowed by a step 302. In step 302, the signal DS start is assigned thelow level since the switching means 202 is activated by the driver, onthe basis of which activation the differential locks are to assume anoperating state other than the non-switched operating state, i.e. are tobe preselected. A first signal level is assigned to the signal DS start,i.e. it is set. In the present case, at least the longitudinaldifferential lock is to be preselected. The step 302 is followed by astep 303 in which the operating mode of the vehicle stabilizing deviceswhich are the vehicle movement dynamics controller and/or electronictraction system and/or traction slip controller and/or braking assistantis influenced, i.e. these vehicle stabilizing devices are deactivated orswitched off. Subsequent to step 303, a step 304 is carried out. In thisstep, the driver is shown, using a display means which is an “ESP-OFF”information light which is arranged in the combination instrument, thatthe vehicle stabilizing devices specified above are deactivated. Thesteps 302, 303 and 304 relate to the preselection of a differentiallock.

Subsequent to the step 304, a step 305 is carried out in which a timeperiod t is compared with a first threshold value ts1. The time period trepresents the time period which has passed between the time at whichthe longitudinal differential lock has been preselected, and the time atwhich the longitudinal differential lock is activated. A value of 5seconds is assumed, for example, for the first threshold value. If thetime period t is shorter than this first threshold value ts1, i.e. ifthe longitudinal differential lock has been activated before the timeperiod represented by ts1 has expired, fault-free operation of thelongitudinal differential lock is occurring, and a step 306 is carriedout adjacent to the step 305. In this step 306, the signal DS active isset, i.e. a first signal level is assigned to it. The signal levelassignment which is carried out in step 306 leads to a situation inwhich, in the subsequent step 307, the brake slip controller isdeactivated in addition to the vehicle stabilizing devices which havealready been deactivated in step 303. In the subsequent step 308, thedeactivation of the brake slip controller is communicated to the driver.This can be done, for example, by means of a corresponding text messagein a multifunctional display and/or by means of a correspondingindicating light. Subsequent to the step 308, a step 318 is carried outwith which the method according to the invention is terminated.

If, in contrast, it is detected in step 305 that the time period t islonger than the first threshold value ts1, i.e. that the longitudinaldifferential lock has not been activated within the time periodrepresented by ts1, it is to be assumed that the fault is possiblypresent during the operation of the longitudinal differential lock. Inthis case, subsequent to the step 305, a step 309 is carried out inwhich the brake slip controller is deactivated in accordance with thestep 307. Subsequent to the step 309, a step 310 is carried out in whichthe driver is informed in accordance with the step 308.

Subsequent to the step 310, a step 311 is carried out in which it ischecked whether the vehicle is moving at a predefined minimum speed. Forthis purpose, the value of the current vehicle speed is compared with acorresponding threshold value vs1, which is, for example, 5 km/h. If thecurrent vehicle speed is lower than the threshold value vs1, the step311 is carried out again. If, in contrast, the current vehicle speed ishigher than the threshold value vs1, a step 312 is carried outsubsequent to step 311. In this step 312, the time period t which hasalready been mentioned above is compared with a second threshold valuets2. This second threshold value has a higher value than the firstthreshold value, for example 30 seconds. If it is detected in step 312that the time period t is shorter than the second threshold value ts2,i.e. if the longitudinal differential lock has been activated before thetime period represented by ts2 has expired, fault-free operation of thelongitudinal differential lock is occurring, for which reason a step 313is carried out subsequent to the step 312. In this step 313, the signalDS active is set in accordance with the procedure in step 306, i.e. thefirst signal level is assigned to said step. In accordance with the step307, this value assignment brings about a situation in which the brakeslip controller is also deactivated. Steps corresponding to the steps307 and 308 have not been inserted at this point in FIG. 3. Subsequentto step 313, the step 318 is carried out.

If, in contrast, it is detected in step 312 that the time period t islonger than the second threshold value ts2, i.e. that the preselectedlongitudinal differential lock has not been activated within the timeperiod represented by ts2 while the vehicle is rolling (see step 311),it must be assumed that there is a fault in the longitudinaldifferential lock or in the lock system. That is to say a mechanicallock problem has occurred. For this reason, a corresponding faultdisplay is issued in the combination instrument, to be more precise in amultifunction display, in step 314 which is subsequent to step 312.Subsequent to the step 314, a step 315 is carried out in which a faultentry is made in the vehicle stabilizing device. The signal DS active isnot set since the longitudinal differential lock is not activated.

Subsequent to the step 315, a step 316 is carried out in which it ischecked whether the signal DS active is still set. If it is detected instep 316 that the signal DS active is still not set, which is equivalentto the longitudinal differential lock still not having been activated,and that consequently a fault is still present in the longitudinaldifferential lock, the step 316 is then carried out again. If, incontrast, it is detected in step 316 that the signal has been set in themeantime, which is equivalent to the longitudinal differential lockhaving been activated in the meantime, and that accordingly it ispossible to assume that the longitudinal differential lock is operatingfree of faults again, a step 317, in which this content is communicatedto the driver by a corresponding display in the combination instrument,is carried out subsequent to the step 316. Subsequent to the step 317,the step 318 is carried out.

By using the method according to the invention described above, it isensured that, even in the case of a line break and/or a line shortcircuit, the operating mode of the vehicle stabilizing devices whichcarry out braking interventions which are independent of the driver inorder to stabilize the vehicle is influenced in good time. In otherwords: if the signals DS-START and/or DS-ACTIVE fail owing to a linebreak or line short circuit, the redundancy of these two signals ensuresthat the vehicle stabilizing devices are switched off or deactivated inall cases. Furthermore, the failure of one of these two signals to occuris detected and a corresponding fault message is triggered in themultifunctional display of the combination instrument.

At this point, it is to be noted that the electronic braking forcedistribution function which is implemented in the vehicle has to beensured even when locks are active. A failure of this function isindicated to the driver.

As is apparent from the statements above, the method according to theinvention which is illustrated in FIG. 3 contains a fault monitoringmeans, which can be used to detect faults which occur at thedifferential locks or which occur owing to the operation of thedifferential locks. This fault monitoring is based on the evaluation oftime windows (steps 305 and 312) in combination with checking of thespeed of the vehicle (step 311).

In particular, owing to the time-based interrogations, a certain amountof time is necessary until it is unambiguously clear whether or not afault is present. For this reason, it is appropriate to use analternative fault monitoring process which dispenses both with thespeed-based and with the time-based interrogations. This alternative,improved fault monitoring process is described below.

The alternative fault monitoring process takes place in the block 202represented in FIG. 2. In addition to the two signals DS start and DSactive, which are generated in any case in the block 202 and are thusavailable in it, a further signal, which is fed to the block 202 fromthe block 203, is evaluated in the block 202 in conjunction with thealternative fault monitoring process. In order to generate this furthersignal, the block 203 requires information about the wheel speeds of theindividual vehicle wheels. Since all the vehicle stabilizing deviceswhich are presented in conjunction with the block 203 have wheel speedsensors, this further signal can be provided by all these vehiclestabilizing devices. However, in what follows it should be assumed thatthis further signal is provided by the vehicle movement dynamicscontroller (ESP) contained in the block 203, but this is not intended tohave a restrictive effect.

Using this further signal, it is communicated to the block 202 that oneof the differential locks, at least the longitudinal differential lockaccording to the above statements relating to FIG. 3, is active. Thisinformation is generated in the block 203 as follows: if a brakingprocess occurs in which the brake slip controller intervenes, i.e. ifbraking interventions are carried out at at least one vehicle wheel insuch a way that this braked wheel is prevented from locking, the wheelspeeds of the wheels of one axle, for example of the front axle or therear axle, are compared with one another. The wheel speeds of the axleon which there is the wheel at which the braking interventions arecarried out within the scope of the brake slip control are preferablycompared with one another. If, for example, the left-hand and theright-hand rear wheels have the same wheel speed, this is a sign thatthe differential lock which is assigned to the rear axle is active. Asstated above, a corresponding evaluation can also be carried out bymeans of the front wheels.

In summary, it is possible to state: when braking with an ABScontroller, an active differential lock can be unambiguously detected bymeans of the distribution of the wheel speed values. An activedifferential lock occurs if the wheel speeds have the same value for atleast one axle of the vehicle, specifically for the axle which isoperatively connected to the active differential lock. Of course, anactive differential lock can also be detected by evaluating all of thewheel speeds. Using the alternative fault monitoring process ensuresthat a corresponding reaction is carried out, associated with acorresponding display, only when an actual fault is detected.

If the alternative fault monitoring process, during which mechanicalcoupling of the axles is detected during an ABS braking maneuver, isused in the method according to the invention, this means, for therepresentation of the method according to the invention in FIG. 3, thatthe steps which relate to the original fault detection, i.e. the steps305 to 317, are to be replaced by steps which relate to the alternativefault detection means. However, at least the steps 305 and 312 whichrelate to the chronological evaluation (stepped time window) and thestep 311, during which a speed-based evaluation takes place, are nolonger necessary.

Essentially, the following sequence of the method according to theinvention is then produced: after the method according to the inventionhas started, both the previous signals DS start and DS active and thefurther signal, which is generated in the block 203 and fed to the block202, are read in and evaluated. Depending on the result which isobtained then, some or all of the vehicle stabilizing devices are thendeactivated and corresponding displays or fault entries are generated.Alternatively, however, all the vehicle stabilizing devices remainactive.

In the original fault monitoring process in which the two signals DSstart and DS active are evaluated in isolation, a malfunction cannot bedetected unambiguously in respect of all possible line faults (linebreak or line short circuit) and/or mechanical faults. This is nowpossible by virtue of the fact that a further signal is evaluated duringthe alternative fault monitoring process.

In the following table 1, all the possible signal states are representedfor the signals DS start and DS active which are to be evaluated duringthe alternative fault monitoring process, as well as the further signalwhich is generated in the block 203 and fed to the block 202 and isdesignated below as DS hard, and said signal states are combined to formeight different system states. The following signal levels are assignedto the values 1 and 0 which are entered in this table: the value “1”corresponds to the low level (2 volts), and the value “0” corresponds tothe high level (4 volts).

TABLE 1 System state DS start DS active DS hard 1 1 1 1 2 1 0 0 3 0 1 14 0 0 1 5 0 0 0 6 1 0 1 7 0 1 0 8 1 1 0

The following table 2 shows which state the individual vehicle deviceswhich are arranged in the vehicle assume in the system states in the toptable 1.

TABLE 2 ESP ASR/ETS ABS BAS System state Active Passive Active PassiveActive Passive Active Passive 1 X X X X 2 X X X X 3 X X X X 4 X X X X 5X X X X 6 X X X X 7 X X X X 8 X X X X

The individual system states will be described below.

System State 1:

In this system state, the vehicle is to travel in a locked fashion, i.e.all the differential locks which are present in the vehicle are activeor activated. This means in turn that, according to the invention, allthe vehicle stabilizing devices are deactivated, i.e. switched to thepassive setting. In this system state there is an option to return tothe normal state (system state 5). The three signals under considerationassume the anticipated values. The driver has preselected thedifferential locks, for which reason the signal DS start has thevalue 1. Owing to the preselection, the differential locks have beenactivated, for which reason the signal DS active has the value 1. Theactivated differential locks are also indicated by the value 1 of thesignal DS hard. The three signals are plausible with respect to oneanother, and consequently there is no fault present.

System State 2:

In this system state, the driver is intended to have preselected thedifferential locks by activating the switching means 202. Thedifferential locks thus assume an operating state other than thenon-switched operating state, but they are not intended to be activeyet. Consequently, the vehicle movement dynamics controller (ESP) andthe traction slip controller (ASR) and the electronic traction system(ETS) and the braking assistant (BAS), of the vehicle stabilizingdevices, are deactivated according to the invention. The brake slipcontroller (ABS) is still active. The three signals under considerationassume the anticipated values. The driver has preselected thedifferential locks, for which reason the signal DS start has thevalue 1. The differential locks are only intended to be preselected inthis system state and not yet activated, for which reason the signal DSactive has the value 0. Since the differential locks are not yetactivated, the signal DS hard also has the value 0. The three signalsare plausible with respect to one another, and consequently there is nofault present.

System State 3:

This system state occurs if the driver would like to change thedifferential locks from the activated state to the deactivated state bycorresponding activation of the switching means 202. The system istherefore in the lock deselection system state.

As long as the differential locks are engaged, i.e. activated, thevehicle stabilizing devices are firstly deactivated according to theinvention, i.e. switched to the passive setting. Immediately after thedriver has initiated the deactivation of the differential locks byactivating the switching means 202, checking is carried out for apredefined time period, which is, for example, 3 seconds, to determinewhether the vehicle is in a stable state or whether the vehicle has astable driving behavior. All the vehicle stabilizing devices are notswitched to the active setting again until this is the case for thepredefined time period. If the vehicle happens to behave in an unstableway during the predefined time period, or if the driving state of thevehicle happens to be unstable during this time period, the checking isstarted again, the vehicle stabilizing devices remain deactivated andthe vehicle behavior is checked again for the predefined time period.

If the vehicle is stationary and the driver switches off the engine inorder to deselect the locking directly after the switching means 202 hasbeen activated, and switches the engine on again directly, the vehiclestabilizing devices at first remain switched to the passive settinguntil the differential locks are disengaged again.

The three signals under consideration assume the anticipated values. Thedriver has activated the switching means 202 in order to initiate thedeactivation of the differential locks, for which reason the signal DSstart has the value 0. Since the differential locks have not yet beendeactivated in the system state under consideration, the signal DSactive has the value 1. In addition, the differential locks which arestill activated are indicated by the value 1 of the signal DS hard. Thethree signals are plausible with respect to one another, andconsequently there is no fault present.

At this point, it is to be noted that the entry in table 2 for the thirdsystem state corresponds to the state of the vehicle stabilizing devicesafter the differential locks have been deactivated. The vehiclestabilizing devices are consequently active again.

System State 4:

The fourth system state is a system state in which the three signalswhich are illustrated in table 1 have implausible values.

If the signal DS hard were to have the correct value, this would meanthat both the signal DS start and the signal DS active would have anincorrect value. There would therefore have to be line interruptionsboth for the signal DS start and for the signal DS active. This wouldmean that there would be a double fault present. However, this cannot bethe case owing to the specific technical embodiment.

Consequently, in the signal combination illustrated in table 1, thesignal DS hard has an incorrect value, and the two signals DS start andDS active have the correct values. That is to say, it is possible toassume that the differential locks have neither been preselected noractivated. For this reason, it is not necessary to deactivate the activevehicle stabilizing devices. For this reason, when the signalcombination which is illustrated for this system state in table 1 ispresent, it is not possible to take any measures to influence thevehicle stabilizing devices. All the vehicle stabilizing devices remainactivated since none of the differential locks can be activated owing tothe signal combination. There is also no fault display in thecombination instrument.

It is also impossible to deactivate the vehicle stabilizing devicesduring an ABS braking operation since the signal DS-START does not havethe value 1 and, accordingly, the checking to determine whether or notthe differential locks are engaged (relates to the steps 303 et seq.illustrated in FIG. 3) is not carried out.

System State 5:

The fifth system state is the normal state in which the driver has notpreselected the differential locks. The differential locks are thus notactive either. Accordingly, according to the invention, all the vehiclestabilizing devices are active.

The three signals under consideration assume the anticipated values.Since the driver has not made any preselection, the signal DS startassumes the value 0. Since the differential locks are not active, boththe signal DS active and the signal DS hard assume the value 0. Thethree signals are plausible with respect to one another and consequentlythere is no fault present.

According to the statements relating to system state 3, this normalstate is not assumed until after a predefined time period during whichthe behavior of the vehicle is checked, starting from the system statein which the differential locks are activated, and accordingly thevehicle stabilizing devices are switched to the passive setting.

System State 6:

In the system state under consideration here, it is assumed that thedriver has preselected the differential locks by activating theswitching means 202. For this reason, the signal DS start has thevalue 1. The differential locks should also be engaged, i.e. active.This is displayed by the value 1 of the signal DS hard. However, thevalue 1 which is anticipated for the signal DS active owing to theactivated differential locks is not present, and instead the signal DSactive has the value 0. For the signal DS active, a line short circuitto the battery voltage (high level, 4 volts) is thus present. That is tosay, in the case of the signal combination illustrated in table 1, thesignal DS active is faulty.

Since the two signals DS start and DS hard have implausible values withrespect to one another, it is firstly assumed that the differentiallocks are in the preselected operating state. Owing to this assumption,the individual vehicle stabilizing devices are placed in the operatingstates, or remain in the operating states, which according to theinvention, they would also assume when the differential locks arepreselected. That is to say, the vehicle movement dynamics controller(ESP) and the traction slip controller (ASR) and the electronic tractionsystem (ETS) and the braking assistant (BAS) are deactivated or remaindeactivated. Only the brake slip controller (ABS) remains active. Thebrake slip controller remains active until a braking operation occurs inwhich the brake slip controller engages and braking interventions areperformed at at least one vehicle wheel in such a way that this brakedwheel is prevented from locking. If, during such a braking operation itis detected, for example by evaluating the wheel speeds, that thedifferential locks are engaged, the brake slip controller is alsoswitched off. However, the brake slip controller is not switched offuntil the time at which the braking interventions which are to becarried out within the scope of the brake slip controller have ended.That is to say, the control process which has begun is still concluded.Hence, in the signal combination illustrated in table 1 for the systemstate 6, the vehicle stabilizing devices are operated as if thedifferential locks were preselected, the driver continues to be providedwith a minimum degree of support because at least the brake slipcontroller is available to him.

After the differential lock is deactivated again, the vehiclestabilizing devices remain deactivated until the next ignition run, anda fault entry is made. In addition, a fault message is displayed in thecombination instrument.

System State 7:

The signal combination illustrated in table 1 indicates an undefinedoperating state since this signal combination cannot be used to inferany definitive information as to whether the differential locks areactivated or deactivated. If this phenomenon occurs after an ignitionrestart, all the vehicle stabilizing devices are immediately temporarilyswitched to the passive setting. This is illustrated in table 2.

If the signal DS active assumes the value 0, which would in fact beanticipated owing to the signal values of the two signals DS start andDS hard, and if the vehicle then behaves in a stable way for apredefined time period which is, for example, 3 seconds, the vehiclestabilizing devices are activated again, i.e. connected into thecircuit.

When the signal combination which is illustrated in table 1 is present,no fault entry is made. The reason for this is as follows: the twosignals DS start and DS active have the same value for each of the twosystem states 3 and 7, and there is no unambiguous information availableabout the operating state of the differential locks.

System State 8:

The eighth system state is a system state in which the three signalsillustrated in table 1 have implausible values.

If the signal DS hard were to have the correct value, this would meanthat both the signal DS start and the signal DS active would have anincorrect value. There would therefore have to be line faults presentboth for the signal DS start and for the signal DS active. This wouldmean that a double fault were present. However, this cannot be the caseowing to the specific technical embodiment.

Consequently, with the signal combination illustrated in table 1, thesignal DS hard has an incorrect value, and the two signals DS start andDS active have the correct value. That is to say it is possible toassume that the differential locks are activated. For this reason, whenthe signal combination illustrated in table 1 is present for this systemstate, the vehicle stabilizing devices are deactivated.

If the signals DE start and DS active assume the value 0 again, and ifthe vehicle then behaves in a stable fashion for a predefined timeperiod, which is, for example, 3 seconds, the vehicle stabilizingdevices are activated again, i.e. connected into the circuit.

The changes in the design of the device according to the invention or inthe sequence of the method according to the invention which result fromthe above statements relating to the alternative fault monitoringprocess have not been taken into account in FIGS. 2 and 3 for reasons ofclarity.

At least one brake slip controller (ABS) and one braking assistant (BAS)and/or one traction slip controller (ASR) and/or one electronic tractionsystem (ETS) and/or one vehicle movement dynamics controller (ESP) areadvantageously arranged in the vehicle as vehicle stabilizing devices.In other words: the vehicle is equipped with a brake slip controller inall cases, and can have any desired combination of the further vehiclestabilizing devices.

1. A device for influencing the operating mode of at least one vehiclestabilizing device of a plurality of vehicle stabilizing devices whichoperate according to different strategies, which actuate, independentlyof the driver, at least brake actuators which are assigned to thevehicle wheels, in order to stabilize the vehicle, and which arearranged in the vehicle, wherein the vehicle has a front axle and a rearaxle and is a two-axle vehicle with all wheel drive in which both thefront axle and the rear axle are each effectively assigned a switchabledifferential lock, wherein a further switchable differential lock isarranged effectively between the front axle and the rear axle, whereinthe differential locks assume, in addition to the non-switched operatingstate, a first operating state which is different from the non-switchedoperating state and in which the differential locks are preselected, anda second operating state which is different from the non-switchedoperating state and the first operating state and in which thedifferential locks are switched, wherein some of the vehicle stabilizingdevices are influenced in terms of their operating mode when the furtherswitchable differential lock arranged effectively between the front axleand the rear axle assumes the first operating state, wherein all thevehicle stabilizing devices are influenced in terms of their operatingmode when the further switchable differential lock assumes the secondoperating state, and wherein the operating mode of the vehiclestabilizing devices is influenced in each case in such a way thatactuation of the brake actuators which are assigned to the vehiclewheels by the respective vehicle stabilizing device independently of thedriver does not occur.
 2. The device as claimed in claim 1, wherein allthe vehicle stabilizing devices which are arranged in the vehicle areinfluenced in terms of their operating mode when the differential lockassumes the first operating state, with the exception of that vehiclestabilizing device which, by actuating the brake actuators independentlyof the driver, prevents the vehicle wheels from locking during a brakingoperation.
 3. The device as claimed in claim 1, wherein, when thedifferential lock changes over from the non-switched operating stateinto the switched operating state which corresponds to the secondoperating state, the first operating state is assumed before the secondoperating state.
 4. The device as claimed in claim 1, wherein at leastone brake slip controller and at least one of a braking assistant, atraction slip controller, an electronic traction system, and a vehiclemovement dynamics controller are arranged in the vehicle as said vehiclestabilizing devices, wherein, if the differential lock assumes the firstoperating state, at least one of the braking assistant, the tractionslip controller, the electronic traction system, and the vehiclemovement dynamics controller is influenced in its operating mode, andwherein, if the differential lock assumes the second operating state, inaddition to the vehicle stabilizing devices whose operating mode wasalready influenced when the differential lock was in the first operatingstate, the brake slip controller is also influenced in terms of itsoperating mode.
 5. The device as claimed 4, wherein, if the differentiallock assumes the second operating state, the brake slip controller andat least one of the braking assistant, the traction slip controller, theelectronic traction system, and the movement dynamics controller areinfluenced in terms of their operating mode.
 6. The device as claimed inclaim 1, wherein the operating state of the differential locks can beset by the driver by activating a switching means, and wherein, at firstthe operating state of the differential lock which is effectivelyarranged between the front axle and the rear axle, then the operatingstate of the differential lock which is effectively assigned to the rearaxle, and then the operating state of the differential lock which iseffectively assigned to the front axle, are set.
 7. The device asclaimed in claim 1, wherein the driver is informed about at least one ofthe operating state of the differential lock, the operating mode of thevehicle stabilizing devices which are arranged in the vehicle, andpossibly occurring faults, by a display means.
 8. The device as claimedin claim 1, wherein at least one signal which represents the operatingstate of the differential lock is generated, and wherein faultmonitoring of the differential lock is carried out as a function of thissignal.
 9. The device as claimed in claim 1, wherein the operating stateof the differential lock can be set by the driver by activating aswitching means, and wherein a fault is detected if, after activation ofthe switching means in order to set an operating state of thedifferential lock which is different from a non-switched operatingstate, a predefined time period has passed without the differential lockassuming this operating state.
 10. The device as claimed in claim 9,wherein, if a first predefined time period has passed without thedifferential lock assuming the second operating state, a vehiclestabilizing device, with which locking of the wheels is prevented duringa braking operation, is influenced in terms of its operating mode. 11.The device as claimed in claim 9, wherein, if a second predefined timeperiod has passed above a predefined vehicle speed without thedifferential lock assuming the second operating state, communication tothe driver is made, a fault entry in a memory medium is made, or bothcommunication to the driver and a fault entry in the memory medium aremade.
 12. The device as claimed in claim 10, wherein, if a secondpredefined time period has passed above a predefined vehicle speedwithout the differential lock assuming the second operating state,communication to the driver is made, a fault entry in a memory medium ismade, or both communication to the driver and a fault entry in thememory medium are made.
 13. A method for influencing the operating modeof at least one vehicle stabilizing device of a plurality of vehiclestabilizing devices which operate according to different strategies,which actuate, independently of the driver, at least brake actuatorswhich are assigned to the vehicle wheels, in order to stabilize thevehicle, and which are arranged in the vehicle, the vehicle having afront axle and a rear axle and being a two-axle vehicle with all wheeldrive in which both the front axle and the rear axle are eacheffectively assigned a switchable differential lock, a furtherswitchable differential lock being arranged effectively between thefront axle and the rear axle, the differential locks assuming, inaddition to the non-switched operating state, a first operating statewhich is different from the non-switched operating state and in whichthe differential locks are preselected, and a second operating statewhich is different from the non-switched and the first operating stateand in which the differential locks are switched, comprising:influencing some of the vehicle stabilizing devices in terms of theiroperating mode when the further switchable differential lock arrangedeffectively between the front axle and the rear axle assumes the firstoperating state, and influencing all the vehicle stabilizing devices interms of their operating mode when the further switchable differentiallock assumes the second operating state, wherein the operating mode ofthe vehicle stabilizing devices is influenced in each case in such a waythat actuation of the brake actuators which are assigned to the vehiclewheels by the respective vehicle stabilizing device independently of thedriver does not occur.